1. Field of the Invention
The invention is an improved method of assembling electric lamps. More specifically, the invention relates to a method of manufacturing high intensity discharge (HID) lamps in which a discharge vessel, such as an arc tube, and frame assembly, when mounted on the lamp stem assembly, are not insertable through the neck portion of an outer envelope.
In the majority of HID lamps, the discharge vessel is arranged in an outer envelope aligned with the lamp axis. The outer envelope has a bulbous portion surrounding the arc tube, and an elongate neck portion extending from the bulbous portion. The arc tube is normally supported in the lamp envelope by a support frame fixed to rigid current-supply conductors extending from the lamp stem through the neck portion.
2. Description of the Prior Art
In manufacturing lamps of this type, a stem assembly is provided which comprises a stem press having a flared skirt, an exhaust tube, and a pair of rigid current-supply conductors extending from the stem press. A discharge device such as an arc tube is then mechanically fixed to the stem assembly by forming a frame including the rigid current-supply conductors, and then attaching the arc tube to the frame. The arc tube is electrically connected to the current-supply conductors either by the mechanical fixation or by auxiliary conductors. The arc tube and frame affixed to the current-supply conductors of the stem assembly are inserted into the bulbous portion of the outer envelope through the open end of the neck portion and aligned with the lamp axis. With the arc tube properly aligned, the flared skirt of the stem press is sealed in a gas-tight manner to the open end of the neck portion.
In certain lamp applications having elongated arcs, it is desirable to have the arc tube oriented at a certain angle with respect to a surface to increase the lighting of that surface. For example, more light will be cast on a playing field if the arc tube is in a horizontal plane than in a vertical plane. However, because existing luminaires at a specific location may be fixed in a predetermined position, it has not been possible to position a standard discharge lamp with the arc tube at the preferred angle with respect to the surface to be illuminated. For example, in sports stadiums the existing luminaires may be fixed at a predetermined position with respect to the playing field or are moveable to only a small degree. Alternatively, mechanical constraints on portable and extendable luminaires, for example in portable light towers for lighting sports fields, may limit the angle at which the luminaire can be supported. As a result, prior art lamps do not provide optimum light distribution when such luminaires are used.
A proposed solution to this problem has been to provide a lamp in which the discharge vessel, such as an arc tube, is supported in the outer envelope at a predetermined angle with respect to the lamp axis. The angle of the arc tube would be chosen such that when the lamp is mounted in a luminaire described above, the arc tube will be at the preferred angle with respect to the surface to be illuminated.
However, in lamps having an arc tube canted more than only a few degrees from the lamp axis, the configuration of the frame for supporting the arc tube has prevented the insertion of the frame and arc tube through the elongate neck portion of the outer envelope. Thus, the known assembly method described above in which the arc tube and frame are secured to the stem assembly prior to insertion into the outer envelope cannot be used. The same problem would occur if it were desired to insert a discharge vessel having a larger diameter than the neck portion of the outer envelope.